Import patches-unapplied version 1:2.10.12-0ubuntu1 to ubuntu/xenial-proposed

Imported using git-ubuntu import.

Changelog parent: ca8405205963e46333cbbe13f7418de78a496288

New changelog entries:
* New upstream version
* debian/patches/python3.patch: updated, upstream fixed purple-url-handler
* debian/patches/gstreamer1.patch,
debian/patches/dtmf-pad.patch:
- removed, the changes are in the new version, including the leakfix
described in lp: #1529445
* debian/libpurple0.symbols: updated